Axiom Home Page Forums General Discussion Home Theater BFD - Anybody care to inform me...

Apparently this little jewel of an electronic device must be worth it's weight in gold upon reading about and seeing all of these graphs concerning the new 800.

Pardon my ignorance but how exactly does this component work, how is it connected and what specific model are you guys referring to? In principal is it like an 'automatic' equalizer?

Is it Behringer or Berringer? I've seen both while searching.

The BFD was intended , as the name implies, to eliminate mics feedback on PA sound systems. It does that by , first finding the offending freq range and then modifying the gain. Feedbacks usually are a very small/narrow area of the freq spectrum. The BFD can zoom in and only affect that offending freq area; that way the overall freq spectrum (sound) doesn't vary significantly.
So , essentially it is a parametric equalizer.

EDIT: I've never used or played with one. That was more or less the answer an sound engineer gave me 15 years ago when I asked him what the BFD was.

Hey Rick - It's Behringer. I'd go loiter around at http://www.hometheatershack.com. That's where the Room EQ Wizard (REW) software resides, as well as kind folks who will dispense the knowledge you seek.

Thanks Tom, I'll get over there and check that out.

My curiosity has been piqued since reading the threads here on the boards.

Edit ... Thanks to you also for the explanation Jaime!

Sucks, doesn't it?

No doubt Tom, just whenever you think all is quiet along the western front.

The BFD is actually quite cheap for the fun and tweakability it offers. I am contemplating putting one on my B-day present list or this years Christmas list as well as a mic to go with it to get better full range readings. What am I getting myself into.

FWIW, I am not finding the BFD to have as much effect as I was led to believe by things I had read.

I had a huge and broad peak at 52Hz: +14db. I thought by eliminating it, I would eliminate some of the boom from my sub and hear a dramatic difference. Surprisingly I heard no obvious difference in music. When switching the filter on and off, the main thing I noticed was that the kick drums got a little louder and quieter.

On HT I used the LOTR Bridge of Khazad Dum scene. Here, because there is so much more bass energy, I could hear a bit more of a difference, but it was quite subtle; sort of like comparing the M22/M60/M80. The LFE for the bridge breaking up and stone crashing into stone sounded a little more well defined and less boomy.

I shouldn't be surprised. Boom and muddyness in bass is caused by the reflection back and forth of frequencies in the room and EQ does not really change this much.

It is also difficult/impossible to EQ a null, because it is caused by cancellation.

Or, maybe I just have tin ears.

Edit: The current model is the DSP1120, I picked up a DSP1100 used. I don't think there is much difference between the two.

Having a sucky room might have something to do with that also

One trick I've found is if you have a null that you can't fix by relocating the sub, you can turn the gain up on the sub and then use the BFD to drop all surrounding frequencies down to the level of the null. This works for me because I need nowhere near the full level of power the EP800 (or 600) provides, so I'm still at < 50% and managed to cut out 1 or 2 nulls that I couldn't get rid of otherwise.

Jason

Jason, if you need no where near the power of either subs, I'll PM you my address and you can send one my way!!

Effing brilliant, Jason.

But now I have to re-do EVERYTHING.

Thanks. I think.

I live to serve Tom.

LMAO ... This is coming from a guy who has not one, but TWO 100+ pound subwoofers to move around.

Now I understand why you guys are using the BFD's.

You should've seen us when we got together to compare the EP600 to the PB13 Ultra. The PB13 weighs more than either of the Axiom subs and is also short and squat and a hell of a lot harder to move. There were three of us pushing it around the room!

Jason for some reason the the visuals on that keep turning into a Three Stooges episode.

Wiseguy, eh?

We actually had four stooges, but our collective girth wouldn't allow all of us to engage the subwoofer simultaneously.

I seem to remember folks recommending against that, but I think it was a headroom issue. I am in the same boat with the EP350 in my room. That takes a lot more filters though doesn't it?

Yes, I think you're right, the main downside is headroom, which I've got boatloads of.

To your second question, in my experience, not necessarily. You can set some pretty "wide" (in octaves) filters that cut down a wide swath of frequencies at once. Of course, the more peaks/nulls you have, the more filters you need, but that's really no different than what you're faced with originally, just that you're setting them in the other direction.

I believe I have 7 running now, and have had up to 13 in the past, which is really just overkill as there is definitely a level of precision beyond which you hear no difference (though the line will continue to flatten).

Jason

I will chime in here.

I use an SVS 16-46 PCi sub. My Behringer DSP-1124P equalizes it to flat within 1db in my room. Here is the way I accomplished it.

First, I downloaded sine waves from the web. I downloaded all sine waves from 16hz to 150hz. I made them into 10 second segments with equal amplitude. I then burned them to CD.

Next, I downloaded the equilization curve for my analog Rat Shack Sound Level Meter. If you have ever used one, you know that they do not measure flat readings...they need to be corrected. I corrrected with the values that can be found (every 5hz), then I interpolated the single hz values in between. I inputted these values into an Excel spreadsheet, hz by hz, so that when I entered the SPL reading into the first column of the spreadsheet, the second column would be the corrected value. This is as accurate as I can get with my equipment.

I then picked a time when nobody was home for a few hours. I played the sine wave CD back at normal listening levels with my speakers off and only the sub running. I recorded the SPL on the spreadsheet, which spit out corrected values. At 10 seconds per tone, this takes about 20 minutes.

Once completed, I looked at the worst area that I found on the spreadsheet. I used the first parametric filter on the BFD to equalize it. This takes time and some math, as it is easy to get the boost or cut correct, but takes a bit of math to get the perfect center frequency, and even more math to get the best bandwidth setting.

Once corrected, I looked for the next worst area and repeated. My first pass used 6 filters. When I thought I had it complete, I ran the test tones again and re-measured. I then found other, new areas that needed correction. That is the cool part of the BFD...you can create a fully parametric filter over the top of one you have already created! My second pass used 7 filters which were much smaller in scope. I ran a third pass with the test tones and found 7 more small areas of correction. My last pas was done and I utilized 4 very small corrections.

When finished, I ran the tones one more time. I was flat from 30-100hz to within 1db, and I was +1.5 db from 30hz down to 18hz, with a dropoff back to average at 16hz. above 100hz, I was within 2db to 150hz. Once I set the crossovers, the upper frequencies went out of play. The lowest octave was boosted because I wanted it just a touch higher, not because I couldn't flatten it any better.

This is a 12 band fully parametric stereo EQ which has the ability to become a 24 band parametric EQ in mono.

Very large room nodes can not be boosted much, so as a previous poster said, you can lower the surrounding areas, then work from there.

Don't get me wrong...first I worked with sub placement and seating placement. Then I worked with room accoustics. The EQ was last, but it does work wonders.

After EQing ths sub, I created another test CD with tones from 20hz to 20khz spaced at 1/6 octave. I used this to EQ my mains, center and surround. I proceeded the same way, but I used digital 31 band Behringer EQs for each channel. Again, only the channel that I was EQing was active, so there was no effect from other speakers or the sub.

Once all of the speakers were EQed, I set the correct levels for each, then set the crossover points. Once finished, it took a few days of listening to get used to the neutral sound. At first, it seemed a bit thin. Once I got used to it, I realized that this is truly what uncolored sound is like. Nuances that I had never noticed before appeared. Everything sounded "alive". The room disappeared.

Switching the EQs off now produces sound that I do not like...at all! Once my ears became trained on the EQed system, I could not go back. Granted, my un-EQed system still sounds better than most of the people we visit, but they generally have small systems thrown together just to have surround sound...some are even cheap boxed systems.

The EQed system is killer, and it all starts with the BFD.

Bill

EDITED for spelling.